Process for the recovery of naphthalene



Dec. 4, 1962 e. SPECKHARDT ETAL 3,0

PROCESS FOR THE RECOVERY OF NAPHTHALENE Filed Sept. 23, 1953 S an R P K6 N/3 A T S 84 E R P 2 3 N A T S E R P FIG. 2

United States Patent Ofifice Patented Dec. 4, 1962 3,067,269 PRGCESS FOR THE RECOVERY {3F NAPHTHALENE Georg Speckhardt, Stolzestrasse 39, and Karlheinz Hennig, Adolf Stoclrerstrasse 7 both of Bochum, Germany Filed ept. 23, 1953, fier. No. 381,780 Claims priority, application Germany Sept. 25, 1952 2 Claims. (Cl. 260-674) In the distillation of coal tar or the like, an oil fraction containing naphthalene is generally produced. This oil fraction is separately subjected to a distillation in which an impure naphthalene is recovered, the solidification point of which may vary within wide limits. For many years, the subsequent further treatment of this impure naphthalene for the purpose of producing pure marketable napthalene has been customary.

The warm crude naphthalene is first freed from phenols and then cooled in vats. When the mother liquor has been drained oif, the crystallised naphthalene is hacked out of the vat, comminuted and centrifuged, whereby a somewhat purer crude naphthalene is obtained. This product is converted under mild heating into a doughy state in which it is introduced in portions into a press having sieve-like walls and a corresponding base. By means of a ram, the material is compressed and the mother solution still adhering to the naphthalene crystals is thus separated off to a considerable extent, while the naphthalene is compressed into the form of a cake. With this method of operation, a pure naphthalene having a solidification point of over 79 C. can be obtained, depending upon the choice of the working temperature. The naphthalene cake removed from the press, which normally has a weight of about 20 kg. and a diameter of about 500 mm. is externally still covered with oil which must be wiped off as far as possible. In order to make this naphthalene ready for dispatch, it must thereafter be suitably comminuted.

After some time, the method was adopted of first freeing this liquid naphthalene-containing oil fraction, which is obtained in the hot state in the distillation of tar, from phenols or the like without the aforesaid intermediate crystallisation and thereafter distilling it in highly selective columns. However, it is thus possible only to produce a naphthalene having a solidification point of about 78 C. The reason for this bad result resides in that during the distillation certain impurities of the naphthalene having the same or substantially the same boiling point are not removed to a sufficient extent, whereby a further increase in the solidification point of the naphthalene is rendered impossible. If it is nevertheless desired to raise the solidification point above about 78 C. it is necessary to effect before the distillation a chemical washing of the naphthalene with sulphuric acid and lye, in which case the impurities boiling with the napthalene are substantially destroyed. It is then possible to obtain a commercial naphthalene having a solidification point of over 78 C. by distilling the said washed material.

Both processes are complicated and costly.

According to the invention warm pressed naphthalene is obtained in a substantially simpler manner, intermediate crystallisation in vats, re-heating and chemical washing of the napthalene with subsequently highly selective distillation being unnecessary.

According to the invention, the crude naphthalene fraction emanating from the distillation of crude tar or oil is worked up directly to form a normal commercial warm pressed material, preferably without previous removal of phenols, by first separating impure solid naphthalene from the starting material by cooling to a suitable temperature below 60 C. and then subjecting the said naphthalene in a lumpy condition, after separation from the mother solution, to a preferably continuous pressing operation in which the material is pressed out in a thin layer with continuous movement. The pressing arrangement advantageously so operates that the naphthalene is compressed to some extent with a kneading action and with a progressive increase of the compressing pressure produced, while the crystals are shifted relatively to one another. The oily impurities are thus substantially eliminated. This pressing arrangement must in additionoperate continuously in order to produce the advantage according to the invention, that is to say, the material continuously fed through the press is also continuously delivered after the pressing. These conditions are fulfilled in an excellent manner by a so-called worm press, the housing of which is fashioned in the manner of a sieve or made permeable to oil.

The starting material, the naphthalene fraction of which is cooled before entering the press to form lumpy naphthalene or a crystal sludge, loses its liquid oily constituents through the perforated casing of the worm press. The pressed material is delivered in a thin layer or in small lumps, the oily impurities being completely uniformly removed by suitable adjustment of the dimensions of the delivery aperture of the press. By choosing a suitable working temperature, it is possible without difficulty to obtain an end product having a solidification point far higher than 79 C. A naphthalene in the form of small lumps is thus obtained, which is marketable without further treatment.

In a continuous pressing operation, a certain temperature increase of the pressed material occurs in the worm press owing to the constant relative movement of the crystals with respect to one another. The value of the said temperature increase is dependent upon the temperature at which the material enters and upon the quantity of oil present in the material. The temperature may be regulated by means of a cooling or heating device which is housed, for example, in the worm shaft and/or in the casing of the press. It is thus possible with a high temperature of admission of the material into the machine to produce an appropriate additional cooling during the pressing operation. Alternatively, if the temperature of admission is low a temperature increase can be produced by means of steam or hot water. It is thus also possible to carry out the pressing, starting with completely solid initial material, without the initial material having first to be brought into a doughy form by a temperature-increase. A means is thus provided of working-up without any special preparation, such as mixing with a fresh fraction, low-grade starting products delivered to the working-up installation. Moreover, it is immaterial whether this material has any water content, since the water-content is pressed out of the crystal mixture together with the oil. On the other hand, naphthalene-containing fractions emanating directly from the distillation may be immediately cooled to a considerable extent by means of a cooling cylinder known in the working-up of coal tar, and the more or less dry crystal sludge thus formed may be Worked up at normal temperature. The provision of a cooling cylinder or the like as described affords, in addition to the possibility of continuously cooling the material as it is produced, the advantage that the quantity of product fed to the press may be regulated by adjusting the speed of the cylinder or the temperature of the cooling water or by regulating the depth of immersion of the cylinder in the oil bath. Instead of the cooling cylinder, cooling drums, cooling worms, mechanical agitating mechanisms, endless cooling belts or the like may be employed. Oils having a low naphthalene content are preferably so prepared for the working-up in the press that the main quantity of the mother solution is removed after the crystallisation by if desired also being heatable.

spe /gee known steps such as filtering, centrifuging, suction filtering and the like. It is particularly expedient in this case to employ a vibrating sieve by means of which the solid crystals may be separated from the liquid. The crystal sludge then formed may then be fed to the continuous press for further working-up, as hereinbefore described.

Instead of the worm press, other pressing apparatus, such as trace presses, displacement centrifuges or worm centrifuges may be employed, which operate with a progressive compression of the material, such arrangements being so operated that the material is moved during the pressing operation and is subjected to the pressure increasein a thin layer.

Examples (1) A naphthalene having a solidification point of 79 C. was obtained after a single passage through the 'worm press from a naphthalene-containing crude oil fraction having a solidification point of 57 C. from which the phenols have not been removed.

(2) The solidification point of a naphthalene fraction from which the phenols had not been removed was raised from 65.9 C. to 79.2 C. when it was passed through the worm press.

(3) Starting with a naphthalene oil fraction having a solidification point of 713 C., from which the phenols had been extracted, and which was crystallised on a cooling cylinder, at pressed material having a solidification point of 795 C. was obtained after the passage thereof through the worm press.

The process according to the invention, may if desired, be combined with further novel steps for the purpose of producing s'o-called pure naphthalene, that is to say, naphthalene of which the solidification point lies above 79 C. and preferably above 80 0, without any chemical treatment having to be applied to the previously purified naphthalene for this purpose.

According to the invention, pure naphthalene (solidi- 'ficati'on point 80 C. or higher) is obtained without chemical reaction and if desired without the usual subsequent re-distillation, by treating the previously purified naphthalene having a solidification point of about 79 C. with a solvent such as benzene or homologues, cooling the solution until lumpy naphthalene crystallises, and working up the naphthalene thereafter in a thin layer by means of the continuous pressing operation hereinbefore described after the solvent has been separated off. Selective solvents, such as methanol or other monovalent or 'polyvalent alcohols, ketones, esters and the like, may

be employed either alone or in mixture and with an addition of water to dissolve the starting material. When such media are employed, the heating or cooling of the solvents may, if desired, be entirely or partially omitted. In any case, however, it is important that the pressing be effected in such manner that it takes place in a thin layer with constant movement of the crystals in relation to one another, preferably by means of a worm press. The material to be pressed is substantially freed very uniformly from the solvent in the press, since the material is in constant motion during the continuous pressing operation and an increasing pressure acts on relatively thin layers of pressed material. Instead of a worm press, other pressing apparatus having a similar operation, for example a trace press, a displacement centrifuge or a worm centrifuge, may be employed provided that the I pressure therein is exerted on relatively thin layers of material.

The installation for carrying out the process consists substantially of a container in which the material to be pressed is mixed with the solvent, the container preferably comprising a mechanical agitating mechanism and The installation further comprises a regulated feed-arrangement which delivers regulated quantities of the material to be treated into the pressing apparatus, a worm press or the like, as well as (:5. the said pressing apparatus itself. The said installation and the process are distinguished by particular simplicity, while in addition occupying little space. It is thus possible under particularly good condition to effect a continuous conversion of crude naphthalene or pre-purified naphthalene into pure naphthalene.

Examples (1) A naphthalene crystal mixture having a solidification point of 70 C. was brought to a solidification of 792 C. by treatment in a worm press, thereafter recrystallised from a mixture of benzene, methanol and water and again pressed in the worm press. The pure naphthalene thus obtained had a solidification point of 79.84 C. On subsequent distillation, the solidification point rose to C.

(2) A naphthalene crystal mixture having a solidification point of 67 C. was pressed in a worm press after cooling with an addition of toluene. The delivered material had a solidification point of 79.5 C. After further recrystallisation and further pressing, the solidification point rose to 79.9 C.

FIGURE 1 of the drawing represents an apparatus for performing the process according to the invention shown as a sectional view.

FIGURE 2 of the drawing shows in diagrammatic form a modification of the procedure of the invention.

The apparatus consists of the screw-press 1 fitted with a conically shaped housing 3, the smaller part extending in direction of the discharge end 2.. The screw 4 is mounted on a hollow shaft 5, passing through the housing 3 of the press at its wider end and being tightened by a stuffing box 6. On the shaft 5 there is fixed atoothed wheel which is driven by a prime mover for the screw-press (not shown). Two pipes 8 and 9 are connected from outside to the hollow shaft of the press serving for the admission or discharge of a liquid or gaseous cooling or heating medium. By suitably adapting the temperature of the medium fed by pipe 8 and drawn-off by pipe 9 it is possible to regulate the temperature of the raw-material to be pressed inside the presshousing according to most favorable degree for pressing.

At the lower part of the press-housing, preferably arranged in horizontal position, there are hole or slot-shaped perforations 10 through which the press oil may run off. The oil is then collected in the trough 11 from which the oil can be drawn-off by pipe 12.

The aperture of the mouth 2 of the press can be calibrated by a mouth-piece 13. This mouth piece 13 is adjusted by means of a spindle 14 in such a way that in the press such pressures are established as required for reaching the desired solidification point of the naphthalene. Whilst the oil separated during the pressing operation is moving towards the wider end of the press and running off through the perforations it the solid naphthalene is conveyed through the mouth 2 to a chute 15 from which it falls onto the conveyer belt 16 transporting the naphthalene to the point for further handling.

The raw-material to be pressed is fed through a feeding hopper 17. To this the raw naphthalene is fed over a chute 18. A cooling drum l9 feeds the raw material to the aforesaid chute 18. The cooling drum 19 consists of a cylindrically shaped metallic drum maintained by inner cooling with water at a temperature below the solidificatron point of the naphthalene, preferably below 60 centigrades. This cooling drum turns at a relatively low speed, e.g. a few revolutions per minute, partially emergmg into a trough 2i filled to a certain level with the liq uid naphthalene oil 21. From the naphthalene oil coming into contact with the cooled drum 19 owing to the low temperature of the drum surface solid naphthalene is sep arated in crystallized form which forms a more or less thick coherent layer on the outside of the cooling drum. This layer is then removed from the cooling drum 19 by a scraper 22 in such a Way that a comparatively coarse maenemas terial is obtained which is fed by way of chute 18 to the feeding hopper 17 and from there to the screw-press.

Referring to FIGURE 2, crude naphthalene is fed through worm press 30 of the same construction as the worm press of FIGURE 1. The oil is expressed in the manner indicated in FIGURE 1. The naphthalene is then dissolved in a solvent in tank 32, recrystallized by cooling the tank and the crystallized naphthalene removed from the tank and pressed continuously in worm press 34 of the same construction as the worm press disclosed in FIGURE 1. The purified naphthalene emerging from worm press 34 is dissolved in the solvent in tank 36 and the naphthalene recrystallized by cooling the tank. The crystals of naphthalene are removed from the tank and passed through worm press 38 to remove solvent and the naphthalene emerging from the press is recoverd.

What we claim is:

1. A process for the production of naphthalene having a melting point above about 79 C. from a mixture consisting essentially of a naphthalene-containing crude oil fraction which, upon cooling to a temperature below 60 C., forms a fluid mixture of naphthalene crystals and mother liquor, said mixture having a melting point substantially below 79 C., comprising cooling the impure mixture to a temperature below about 60 C. at which crystallized naphthalene is formed, separating the naphthalene crystals from the mother solution, subjecting the naphthalene so separated and still containing oil which adheres to the naphthalene and in lumpy form to a continuous kneading action while simultaneously advancing it under progressively increasing pressure through a channel, the walls of which have apertures, and simultaneously expressing the oil from the naphthalene through said apertures in the walls of the channel, said pressure being sufficient to simultaneously express substantially all of the oil from the naphthalene so that, by the time the naphthalene has advanced completely through the channel, it has a melting point above about 79 C.

2. A process for the production of naphthalene having a melting point above about 79 C. from a mixture consisting essentially of a naphthalene-containing crude oil fraction which, upon cooling to a temperature below 60 C., forms a fluid mixture of naphthalene crystals and mother liquor, said mixture having a melting point substantially below 79 0., comprising cooling the impure mixture to a temperature below about 60 C. at which crystallized naphthalene is formed, separating the naphthalene crystals from the mother solution, subjecting the naphthalene so separated and still containing oil which adheres to the naphthalene and in the form of a dry sludge to a continuous kneading action While simultaneously advancing under progressively increasing pressure through a channel, the walls of which have apertures, and simultaneously expressing the oil from the naphthalene through said apertures in the walls of the channel, said pressure being suflicient to simultaneously express substantially all of the oil from the naphthalene so that, by the time the naphthalene has advanced completely through the channel, it has a melting point above about 79 C.

References Qited in the file of this patent UNITED STATES PATENTS 675,179 Wacker May 28, 1901 2,078,963 Miller May 4, 1937 2,321,117 Wilcock June 18, 1943 2,701,518 McDonald Feb. 8, 1955 FOREIGN PATENTS 255,429 Great Britain June 23, 1927 493,992 Great Britain Oct. 18, 1938 380,990 Great Britain Sept. 29, 1932 

1. A PROCESS FOR THE PRODUCTION OF NAPHTHALENE HAVING A MELTING POINT ABOVE 79*C. FROM A MIXTURE CONSISTING ESSENTIALY OF A NAPHTHALENE-CONTAINING CRUDE OIL FRACTION WHICH, UPON COOLING TO A TEMPERATURE BELOW 60* C., FORMS A FLUID MIXTURE OF NAPHTHALENE CRYSTALS AND MOTHER LIQUOR, SAID MIXTURE HAVING A MELTING POINT SUBSTANTIALLY BELOW 79*C., COMPRISING COOLING THE IMPURE MIXTURE TO A TEMPERATURE BELOW ABOUT 63*C. AT WHICH CRYSTALLIZED NAPHTHALENE IS FORMED, SEPARATING THE NAPHTHALENE CRYSTALS FROM THE MOTHER SOLUTION,SUBJECTING THE NAPHTHALENE SO SEPARATE AND STILL CONTAINING OIL WHICH ADHERS TO THE NAPHTHALENE AND IN LUMPY FORM TO A CONTINUOUS KNEADING ACTION WHILE SIMULTANEOUSLY ADVANCING IT UNDER PROGESSIVELY INCREASING PRESSURE THROUGH A CHANNEL, THE WALLS OF WHICH HAVE APERTURES, AND SIMULTANEOUSLY EXPRESSING THE OIL FROM THE NAPHTHALENE THROUGH SAID APERTURES IN THE WALLS OF THE CHANNEL, SAID PRESSURE BEING SUFFICIENT TO SIMULTANEOUSLY EXPRESS SUBSTANTIALY ALL OF THE OIL FROM THE NAPHTHALENE SO THAT, BY THE TIME THE NAPHTHALENE HAS ADVANCED COMPLETELYTHROUGH THE CHANNEL, IT HAS A MELTING POINT ABOVE ABOUT 79*C. 